The present invention generally relates to a method of using additive manufacturing processes to produce reinforced ceramic or ceramic composite materials, such as but not limited to ceramic-ceramic or ceramic-metal hybrid (i.e., cermet) materials.
Many modern engines and next generation turbine engines require components and parts having intricate and complex geometries, which require new types of materials and manufacturing techniques. One such material includes ceramic components and parts, which reduce the need for cooling and are much lighter than conventional alloy materials in current engines. Integration of ceramics into next generation engine thus has the advantages of being lighter, chemically inert, and highly heat resistant. However, ceramics are also known to be weak in shearing and tension, and too brittle for use in certain applications. Thus, there is a need to develop new ceramic composites and methods of manufacturing these ceramic parts.
Conventional techniques for manufacturing engine parts and components involve the laborious process of investment or lost-wax casting. One example of investment casting involves the manufacture of a typical rotor blade used in a gas turbine engine. A turbine blade typically includes hollow airfoils that have radial channels extending along the span of a blade having at least one or more inlets for receiving pressurized cooling air during operation in the engine. Among the various cooling passages in the blades, includes serpentine channel disposed in the middle of the airfoil between the leading and trailing edges. The airfoil typically includes inlets extending through the blade for receiving pressurized cooling air, which include local features such as short turbulator ribs or pins for increasing the heat transfer between the heated sidewalls of the airfoil and the internal cooling air.
The manufacture of these turbine blades, typically from high strength, superalloy metal materials, involves numerous steps. First, a precision ceramic core is manufactured to conform to the intricate cooling passages desired inside the turbine blade. A precision die or mold is also created which defines the precise 3-D external surface of the turbine blade including its airfoil, platform, and integral dovetail. The ceramic core is assembled inside two die halves which form a space or void therebetween that defines the resulting metal portions of the blade. Wax is injected into the assembled dies to fill the void and surround the ceramic core encapsulated therein. The two die halves are split apart and removed from the molded wax. The molded wax has the precise configuration of the desired blade and is then coated with a ceramic material to form a surrounding ceramic shell. Then, the wax is melted and removed from the shell leaving a corresponding void or space between the ceramic shell and the internal ceramic core. Molten metal is then poured into the shell to fill the void therein and again encapsulate the ceramic core contained in the shell. The molten metal is cooled and solidifies, and then the external shell and internal core are suitably removed leaving behind the desired metallic turbine blade in which the internal cooling passages are found.
The cast turbine blade may then undergo additional post casting modifications, such as but not limited to drilling of suitable rows of film cooling holes through the sidewalls of the airfoil as desired for providing outlets for the internally channeled cooling air which then forms a protective cooling air film or blanket over the external surface of the airfoil during operation in the gas turbine engine. However, these post casting modifications are limited and given the ever increasing complexity of turbine engines and the recognized efficiencies of certain cooling circuits inside turbine blades, the requirements for more complicated and intricate internal geometries is required. While investment casting is capable of manufacturing these parts, positional precision and intricate internal geometries become more complex to manufacture using these conventional manufacturing processes. Accordingly, it is desired to provide an improved casting method for three dimensional components having intricate internal voids.
Additive manufacturing processes have simplified the above described process by allowing the manufacture of synthetic model casting. In particular, a model of a component may be created by additive manufacturing techniques or 3D printing. A core is cast inside a synthetic model. The synthetic model may then be removed from the cast core, and then the cast core is used for casting an authentic component therearound. The core is removed from inside the authentic component, with an authentic component precisely matching the original synthetic model. This technology effectively creates a disposable core die (or “DCD”). U.S. Pat. No. 7,413,001 describes one application of this process.
The immediate application of this DCD technology allows the industry to produce complex components, structures, and parts using new combinations of materials or hybrid materials that can be incorporated into next generation engines. The DCD process has been demonstrated with success to accomplish this endeavor by utilizing additive manufacturing methods to produce master dies or DCDs that have geometries not previously achieved or at the very least more efficiently than previously accomplished through conventional investment casting processes.
The present invention applies the DCD additive printing technologies previously described to create a new family of hybrid materials and functional components that were previously never possible to produce by conventional manufacturing processes. In particular, the current invention overcomes the problems associated with investment and/or lost-wax casted products that lack intricate or complex internal geometries, cavities, or hollows. Particularly valuable materials would be ceramic-ceramic and ceramic-metal composite/hybrid systems. The present invention also solves some of the problems associated with conventional casting techniques, such as but not limited to core kissout, tipping, cracking scraps.